Chandra spectroscopy of Rapid Burster type-I X-ray bursts

TL;DR

This study used Chandra to observe the Rapid Burster during a specific state, detecting 20 type-I X-ray bursts and searching for spectral features to understand neutron star properties, but found none.

Contribution

First high-resolution spectroscopic observation of the Rapid Burster's type-I X-ray bursts in the 'banana' state, setting upper limits on spectral features.

Findings

Detected 20 thermonuclear X-ray bursts with recurrence times of 0.9-1.2 hours.

No narrow spectral features were observed in the burst emission.

Upper limits on absorption lines and edges are consistent with theoretical predictions.

Abstract

We observed the Rapid Burster with Chandra when it was in the 'banana' state that usually precedes the type-II X-ray bursting 'island' state for which the source is particularly known. We employed the High-Energy Transmission Grating Spectrometer in combination with the ACIS-S detector in continuous clocking mode. The observation yielded 20 thermonuclear type-I X-ray bursts emitted from the neutron star surface with recurrence times between 0.9 and 1.2 hr, and an e-folding decay time scale of 1 min. We searched for narrow spectral features in the burst emission that could constrain the composition of the ashes of the nuclear burning and the compactness of the neutron star, but found none. The upper limit on the equivalent width of narrow absorption lines between 2 and 6 keV is between 5 and 20 eV (single trial 3 sigma confidence level) and on those of absorption edges between 150 and 400 eV. The latter numbers are comparable to the levels predicted by Weinberg, Bildsten & Schatz (2006) for Eddington-limited thermonuclear bursts.